a) Field of the Invention
This invention relates to a control device for an electric generator (such as an alternator) for use with a vehicle engine. In preferred embodiments, this invention relates to a control device in which a generator field winding current is controlled in response to an electric load condition or, when used with an automobile, to an operating condition of the automobile.
b) Description of Related Art
It is known from JP-A-59-76198 (1984) to provide a control device for an electric generator in which the field current is controlled so that the output voltage of the generator reaches a target voltage determined in response to a load.
Further, JP-A-55-29222 (1980) discloses detecting the field current of a generator and controlling the field current to reach a predetermined value.
It is also known from JP-A-59-83600 (1984) that during a sudden load change a voltage command value may be changed in a step toward a target voltage to change the generator field current also in a step.
Moreover, JP-B-1-56617 discloses the use of a microcomputer to optionally control the power generation condition of a generator in response to, for example, the load condition and the battery condition of a vehicle.
In the above-mentioned JP-A-59-76198 (1984), the field current is controlled in an open-loop manner, but a problem arises in that the variation of the field current due to, for example, the condition of the current supply source and the resistance change of a field coil, is uncontrollable. Namely, there is a problem, in that, even if there is no change in the target voltage, the target voltage cannot be maintained if the field current change due to, for example, a change in the field winding resistance caused by ambient temperature change and increase in field winding temperature.
In the above noted JP-A-55-29222 (1980), although the field current is feedback-controlled, the feedback control is effected so that the output voltage of the generator is always kept at a predetermined value, but such is inapplicable to obtaining output voltage control in response to a load variation. Further, in this reference, because the field current is detected by a current transformer, there is a problem, in that, it is unsuitable for forming the circuit into an integrated circuit (IC).
In JP-A-59-83600 (1984), the control ratio is limited near a practical output voltage value of the generator and a comparatively broad band level of control cannot be obtained. In this respect, this known device is only effective to abruptly change the generator torque, by cutting the generator field current off. Therefore, the problem exists that the torque variation to drive the generator cannot be adequately controlled. Thus, when a large resistance load such as an air-conditioner is switched on, the power required from the generator suddenly increases, resulting in increase in the torque required to drive the generator which, in an automobile, increases the torque requirement from the internal combustion engine. If the engine is running at idling speed, the increase in torque required to drive the generator can stall the engine. In other words, the load increase occurs too suddenly for the fuel-injection system of the engine to react to increase the amount of fuel required to drive the engine to satisfy the torque required to drive the generator. In the prior art reference, the alternator torque is suddenly increased in one step leading to possible stalling of the automobile engine. Further, in this reference and JP-B-1-56617 when power generation is required to be controlled in response to the load condition and the battery condition of a vehicle, there is a problem in that the required control cannot be achieved as required because of internal factors within the disclosed circuits, such as change of the field coil resistance.
The present invention seeks to overcome the foregoing disadvantages.
An object of the present invention is to enable the output voltage of a generator to be controlled over a broad range in response to changing load by feedback-control of the field winding current and so that the field winding current is not affected by the condition of the current supply (battery) source or the resistance change of the field coil.
A further object of a feature of the present invention is to effectively lessen variation in the torque required to drive the generator with variation of load.
Still another object of a further feature of the present invention is to precisely control the field current according to the power generation condition in response to the load condition and the battery condition of the vehicle.